The present invention relates to acoustics, more particularly to utilization of walls and other barriers to isolate acoustic transmission in one space or to reduce or minimize acoustic transmission from one space to another.
Conventional walls are flat structures that reflect some acoustic energy and transmit some acoustic energy. Typical walls used today are straight and flat. The materials of the walls currently used are typically drywall, which is a gypsum-type board. In general, the more stiff (less flexible) and the more massive a wall, the greater the acoustic attenuation.
In a typical present-day environment of an office or home, a wall is constructed using wood studs and ½-in drywall attached to the studs with nails or screws. One piece of drywall is placed on each side of the room. The drywall has two layers and provides attenuation whereby sound waves travel from one room through the first layer of drywall, and then the second layer of drywall, and then into the adjoining room. To increase the acoustic attenuation, ¾-in drywall may be used in lieu of ½-in drywall. In a typical present-day industrial environment, metal walls that are straight, flat, and thin are implemented along with sound-absorbing foam/fiberglass/mineral wool. A rubber barrier lined with foam may also be used. Various wall constructions for home, office, and industrial use are commercially available and in current use.
Two important terms that describe sound reduction of walls are “Transmission Loss” (“TL”) and “Sound Transmission Class” (“STC”). These are among several terms conventionally used to describe the level of attenuation that occurs across a wall. Transmission loss is the reduction in acoustic power from one side of a wall to the other, and is expressed in dB. The higher the TL number, the greater the reduction in sound transmission. Transmission loss is frequency-dependent, and as such it is commonly plotted versus frequency. An alternative designation for describing sound reduction is sound transmission class, a single number that can conveniently represent how well a particular wall performs as compared with another wall.
Various factors limit the effectiveness of the conventional flat-plate wall design. Generally speaking, transmission loss is worst (lowest) at the fundamental resonant frequency of the plate. An additional factor is performance versus weight. In order to gain an increase in performance of a conventional flat-plate design, one must increase thickness and/or change the material.